1. Field of the Invention
The present invention relates to a method of manufacture of solenoidal magnet coils, and to solenoidal magnet coils themselves. In particular, it relates to such coils for generating high strength magnetic fields, which may be applied in systems such as nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI).
2. Description of the Prior Art
FIGS. 1A-1B illustrate cross-sectional and axial sectional views, respectively, of a conventional solenoidal magnet arrangement for a nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) system. A number of coils of superconducting wire are wound onto a former 1. The resulting assembly is housed inside a cryogen vessel 2 which is at least partly filled with a liquid cryogen 2a at its boiling point. The coils are thereby held at a temperature below their critical point.
The former 1 is typically constructed of aluminum, which is machined to ensure accurate dimensions of the former 1, in turn ensuring accurate size and position of the coils which are wound onto the former. Such accuracy is essential in ensuring the homogeneity and reliability of the resultant magnetic field. Superconducting magnets may quench due to even a small amount of movement of even one turn of the coil. The formers must therefore be very rigid. These requirements combine to render the production of formers very expensive.
Also illustrated in FIGS. 1A-1B are an outer vacuum container 4 and thermal shields 3. As is well known, these serve to thermally isolate the cryogen tank from the surrounding atmosphere. Insulation 5 may be placed inside the space between the outer vacuum container and the thermal shield. However, as can be seen in FIGS. 1A-1B, these elements also reduce the available inside diameter 4a of the solenoidal magnet. Since the inside diameter 4a of the solenoidal magnet is required to be of a certain dimension to allow patient access, the presence of the outer vacuum container 4 and the thermal shields 3 effectively increases the diameter of the magnet coils and the former 1, adding to the cost of the overall arrangement.
The cost of producing a former 1 such as illustrated in FIGS. 1A-1B and described above is accounted for approximately equally by labor costs and material costs. Among other objectives, the present invention seeks to reduce the labor costs involved in producing a solenoidal magnet structure.
U.S. Pat. No. 5,917,393 describes a solenoidal superconducting magnet arrangement wherein the various coils are mounted on an inner or outer surface of a thermally conductive cylindrical former, whereby cooling may be applied through the material of the former. The coils are thermally connected to, but electrically isolated from, the material of the cylindrical former.